Solar tracking system

ABSTRACT

A solar tracking system enables an array of solar panels to track a path of the sun. The system includes a main support arm ( 205 ) having a hub end and a distal end. A rotatable main hub ( 220 ) is attached to the hub end of the main support arm ( 205 ). A support frame ( 215 ) is rotatably attached to the distal end of the main support arm ( 205 ). A tie-rod ( 210, 610 ) includes a swivel end and a frame end, and the swivel end is rotatably positioned adjacent to the main hub ( 220 ). The frame end of the tie-rod ( 210, 610 ) is connected to the support frame ( 215 ) above the distal end of the main support arm ( 205 ), such that rotation of the main hub ( 220 ) causes a vertical orientation of the support frame ( 215 ) to change.

FIELD OF THE INVENTION

The present invention relates to mechanisms for tracking movement of thesun. In particular, although not exclusively, the invention relates to asystem for maintaining one or more solar panels facing the sun duringthe day to improve solar energy collection efficiency.

BACKGROUND TO THE INVENTION

Global warming and the increase in greenhouse gas emissions haveresulted in an increased public awareness of solar energy use. Further,advanced technology has enabled the use of solar energy in residentialand small scale commercial buildings to become more economicallyfeasible. In particular, the costs of photovoltaic panels have decreasedwhile operating efficiencies of such panels have significantlyincreased.

Other technologies associated with solar panels have also advanced. Forexample, various companies have attempted to improve mounting andtracking capabilities of solar panels. It is well known that when asolar panel is enabled to track the movement of the sun from east towest—so that a normal vector extending from a plane of the solar panelalways remains pointed at the sun—the amount of energy collected by thesolar panel can be greatly improved. Energy collection efficiencyassociated with a tracking solar panel can be almost 60% higher than anefficiency of a similar panel that is simply mounted in a staticposition. A solar panel that tracks the sun generally must be pivotedabout at least two axes: a first axis that pivots horizontally from eastto west; and a second axis that pivots vertically upward from thehorizon during the morning and downward toward the horizon during theafternoon.

The prior art therefore includes numerous devices and systems designedto enable a solar panel to track the movement of the sun. For example,such prior art includes the following:

U.S. Pat. No. 4,295,621 to Siryj, B, filed Mar. 18, 1980, titled “SolarTracking Apparatus”, discloses a solar array support member pivotallysecured to the upper end of a support post for rotation about ahorizontal axis. The support post is driven about a vertical axis. Amotor and pulley system drive a rotating disc secured to the post to setthe elevation position of the support member. A second motor and pulleysystem drive the post about its vertical axis with respect to a base.

U.S. Pat. No. 4,368,962 to Hultberg, D, filed Jan. 30, 1981, titled“Solar Tracking Apparatus and System”, discloses an apparatus comprisinga pair of concentric shafts oriented parallel to the earth's rotationalaxis with one shaft being rotated by a motor at one revolution per day,so that a yoke rigidly attached to the shaft will follow the diurnalmotion of the sun. A second concentric shaft is rotated at a raterelative to the first shaft and, by means of a spherical four-barlinkage, automatically produces a rotational oscillation of a support orgimbal mounted on the yoke equal to the yearly declination of the sun.

International application PCT/DE94/00612 to Berger, A., filed Jun. 1,1994, titled “Sun-Following Device”, discloses the use of anenergy-storing counterweight in a base of a first solar panel that ishydraulically linked to an energy-storing counterweight in a base of asecond solar panel. The counterweights are attached to linkageassociated with their respective solar panels to enable movement of thesolar panels.

U.S. Pat. No. 6,848,442 to Haber, M. filed Jan. 29, 2001, titled “SolarPanel Tilt Mechanism”, discloses a tilt mechanism associated with anarray of solar panels whereby effort required to tilt the solar panelsis reduced by appropriate placement of first and second tilt axes withrespect to the centre of mass and/or centre of pressure of the panelsdue to wind.

U.S. Pat. No. 6,443,145 to Buron, V. et al., filed Aug. 24, 2001, titled“Solar Seeker”, discloses a solar panel carriage assembly, a mountingassembly, and a travel assembly to enable a solar panel to automaticallytrack the sun.

However, the prior art devices and systems described above generallyrequire either complex components such as multiple motors or hydraulicsystems, non-durable components such as numerous small gearingmechanisms, or single-panel specific components that cannot be easilylinked to move multiple panels in a solar panel array. Further, motionof some prior art sun tracking systems is restricted so that only apartial path of the sun when above the horizon can be tracked. There istherefore a need for an improved solar tracking system that overcomesone or more of these disadvantages.

OBJECTS OF THE INVENTION

Therefore, an object of some embodiments of the present invention is toovercome or alleviate one or more limitations of the prior art,including providing an improved solar tracking system.

Another object of some embodiments of the present invention is toprovide an improved solar tracking system that includes durable androbust components that enables a long, low-maintenance service life.

Another object of some embodiments of the present invention is toprovide an improved solar tracking system that can move multiple solarpanels arranged in an array.

Another object of some embodiments of the present invention is toprovide an improved solar tracking system that can move multiple solarpanels through multiple degrees of freedom using only a single drivemechanism.

A further object of some embodiments of the present invention is toprovide an improved solar tracking system that enables attached solarpanels to deflect in high winds, thereby reducing wind-induced forces onassociated mounting hardware.

Still another object of some embodiments of the present invention is toprovide an improved solar tracking system that enables a solar panel tobe positioned fully vertically to point directly at the horizon, thusenabling increased energy collection efficiency during the early morningand late afternoon. Still further objects will be evident from thefollowing detailed description.

SUMMARY OF THE INVENTION

According to one aspect, the present invention is a solar trackingsystem, comprising:

a main support arm having a hub end and a distal end;

a rotatable main hub attached to the hub end of the main support arm;

a support frame rotatably attached to the distal end of the main supportarm; and

a tie-rod having a swivel end and a frame end, the swivel end rotatablypositioned adjacent to the main hub and the frame end connected to thesupport frame above the distal end of the main support arm, wherebyrotation of the main hub causes a vertical orientation of the supportframe to change.

Optionally, the tie-rod comprises a spring mechanism.

Optionally, the swivel end of the tie-rod is connected to a tie-rodbracket extending from a centre post of the main hub, wherein the mainhub is rotatable relative to the centre post.

Optionally, the support frame comprises a solar panel support frame.

Optionally, the main hub comprises a pulley or sprocket for causingrotation of the main hub.

Optionally, the solar tracking system further comprises an arrayincluding a plurality of main hubs supporting a plurality of supportframes, wherein each main hub in the plurality of main hubs is attachedto a central support rail.

Optionally, the swivel end of the tie-rod is connected to a rear pillarmount.

Optionally, the solar tracking system further comprises a clampingsleeve for attaching the rear pillar mount to a support rail, andanother clamping sleeve for attaching the main hub to the support rail.

Optionally, a distance between the main hub and the rear pillar mount isadjustable.

Optionally, the solar tracking system further comprises a ball joint atthe swivel end of the tie-rod and a ball joint at the frame end of thetie-rod.

Optionally, a length of the tie-rod is adjustable.

Optionally, a distance between the main hub and the rear pillar mount isadjustable.

Optionally, the solar tracking system further comprises an electricmotor to power a drive cable or sprocket engaging the main hub.

Optionally, the electric motor is controlled by a timer or a positionsensor.

Optionally, the main support arm, the rotatable main hub, the supportframe, and the tie-rod define a pivotable base mechanism.

BRIEF DESCRIPTION OF THE DRAWINGS

To assist in understanding the invention and to enable a person skilledin the art to put the invention into practical effect, preferredembodiments of the invention are described below by way of example onlywith reference to the accompanying drawings, in which:

FIG. 1 is a diagram illustrating a top perspective view of a solar panelarray, including a plurality of pivotable base mechanisms, mounted on aroof of a building such as a house in the southern hemisphere, accordingto some embodiments of the present invention.

FIG. 2 is a diagram illustrating a close-up, top view of a pivotablebase mechanism of FIG. 1.

FIG. 3 is a diagram illustrating a close-up, side view of a pivotablebase mechanism of FIG. 1.

FIG. 4 is a diagram illustrating a close-up, top view of a pivotablebase mechanism aligned in the same orientation shown in FIG. 3.

FIG. 5 is a diagram illustrating a close-up, rear view of a pivotablebase mechanism of FIG. 1.

FIG. 6 is a diagram illustrating a close-up, side view of a pivotablebase mechanism, according to some alternative embodiments of the presentinvention.

FIG. 7 is a diagram illustrating a close-up, partial cut-away view of alinear spring gas strut tie-rod, according to some embodiments of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention comprise a solar tracking system.Elements of the invention are illustrated in concise outline form in thedrawings, showing only those specific details that are necessary tounderstanding the embodiments of the present invention, but so as not toclutter the disclosure with excessive detail that will be obvious tothose of ordinary skill in the art in light of the present description.

In this patent specification, adjectives such as first and second, upand down, above and below, top and bottom, etc., are used solely todefine one element or method step from another element or method stepwithout necessarily requiring a specific relative position or sequencethat is described by the adjectives. Words such as “comprises” or“includes” are not used to define an exclusive set of elements or methodsteps. Rather, such words merely define a minimum set of elements ormethod steps included in a particular embodiment of the presentinvention.

Referring to FIG. 1, a diagram illustrates a top perspective view of asolar panel array 100 mounted on a roof 105 of a building such as ahouse in the southern hemisphere, according to some embodiments of thepresent invention. The solar panel array 100 includes five solar panels110-n (i.e., 110-1 through 110-5) that are shown pivoted to anear-vertical position facing to the East. As shown, the solar panels110-n are ready to receive sunlight from the north-eastern horizonduring the early morning. Each solar panel 110-n is attached to apivotable base mechanism 115-n that enables the solar panels 110-n topivot simultaneously about both a horizontal and a vertical axis totrack the position of the sun from when, for example, it rises in theNortheast to when it sets in the Northwest during winter in the southernhemisphere.

A drive cable 120 is shown engaging each of the pivotable basemechanisms 115-n. A cable actuator 125 is also connected to the drivecable 120 and powers movement of the drive cable 120. The cable actuator125 includes an electric motor 130 and a controller and can be mounted,for example, on the roof 105 or on one of a plurality of supportbrackets 145.

A central support rail in the form of a central support pipe 140, suchas a standard steel plumbing pipe, is mounted to the roof 105 using thesupport brackets 145, and extends beneath each pivotable base mechanism115-n. Each pivotable base mechanism 115-n is then clamped to thecentral support pipe 140. A light sensing electronic eye 150, which arewell known by those having ordinary skill in the art, can be mounted onone of the solar panels 110-n, such as on the solar panel 110-1, toenable automatic determination of a present position of the sun. Also, atimer can be mounted on one of the solar panels 110-n to time movementof the pivotable base mechanisms 115-n. The electronic eye 150 and thetimer can be operatively connected to the controller 135 using wired orwireless connection means.

Referring to FIG. 2, a diagram illustrates a close-up, top view of oneof the pivotable base mechanisms 115-n, according to some embodiments ofthe present invention. The pivotable base mechanisms 115-n each includea main support arm 205, a tie-rod 210, and a solar panel support frame215. For clarity, in FIG. 2 and all subsequent figures the solar panel110-n is removed from the solar panel support frame 215 and is notshown. The main support arm 205 is attached at a hub end to a main hub220, which is bolted to the central support pipe 140. A distal end ofthe main support arm 205 is attached to the solar panel support frame215. The main support arm 205 thus, in use, supports the weight of thesolar panel support frame 215 and an attached solar panel 110-n, and canrotate relative to the central support pipe 140. The drive cable 120 iswrapped around and engages a pulley 225 attached to the main hub 220,and thus linear movement of the drive cable 120 causes rotationalmovements of the main hub 220 and the main support arm 205. Further,bearings 230 at the distal end of the main support arm 205 enablepivoting of the solar panel support frame 215 between vertical andhorizontal orientations.

A first ball joint 235 at a swivel end of the tie-rod 210 is connectedto a distal end of a tie-rod bracket 239 that is fixed relative to thecentral support pipe 140. A second ball joint 240 at a frame end of thetie-rod 210 is bolted to the solar panel support frame 215 above thebearings 230. Frame flanges 245 are used to bolt a solar panel 110-n tothe solar panel support frame 215.

As described in more detail below, the tie-rod 210 may comprise a linearspring to enable the solar panels 110-n to lean over under high winds,and thus reduce high wind forces on the solar panel array 100, whichforces otherwise could potentially damage the solar panels 110-n, thepivotable base mechanisms 115-n, or roofing structures to which thesupport brackets 145 are attached.

Referring to FIG. 3, a diagram illustrates a close-up, side view of oneof the pivotable base mechanisms 115-n, according to some embodiments ofthe present invention. The pivotable base mechanism 115-n is shownrotated relative to the central support pipe 140 so that the mainsupport arm 205 and the tie-rod 210 are both parallel to each other andparallel to the central support pipe 140 in a vertical plane. Suchrotation away from the position shown in FIG. 2 causes a distancebetween the first ball joint 235 and the bearings 230 at the distal endof the main support arm 205 to increase. That in turn causes the secondball joint 240 to pull on a bracket 300 of the solar panel support frame215 and pivot the solar panel support frame 215 backward about thebearings 230 and to a position, as shown, about 45 degrees between thevertical and horizontal.

Shown in a partial cut-away view of the main hub 220, a main hub bolt305 secures the tie-rod bracket 239 above the main hub 220, whichenables the tie-rod 210 to swing over the main hub 220. The main hubbolt 305 bolts directly to a hub post 325. A clamping sleeve 320 weldedto the hub post 325 is used to clamp the hub post 325 to the centralsupport pipe 140 using bolts 330. Bearings 335 inside the main hub 220enable the main support arm 205 to rotate relative to the hub post 325;whereas the tie-rod bracket 239 is rigidly connected to a clampingcollet 336 that fits over the hub post 325. The tie-rod bracket 239 thusremains generally parallel to the central support pipe 140 in a verticalplane.

A distance between the main hub 220 and the swivel end of the tie-rod210 thus remains substantially constant when the main hub 220 rotatesrelative to the central support pipe 140.

The clamping collet 336 also secures the bearings 335 to the hub post325. The clamping collet 336 is driven between a bearing radius corner338 and the hub post 325 and prevents the tie-rod bracket 239 fromrotating relative to the central support pipe 140. Releasing the mainhub bolt 305 enables the tie-rod bracket 239 to be rotated around thehub post 325 to locate, for example, a North position in Southernhemisphere locations.

The orientation of the pivotable base mechanism 115-n shown in FIG. 3 isthus used, for example, around noon when the sun is highest in the skyand is shining from the North (in the Southern hemisphere). Depending onthe season and the latitudinal position of the pivotable base mechanism115-n, increasing an effective length of the bracket 300 (e.g., byloosening a bolt through the second ball joint 240 and sliding the boltin a slot 337 in the bracket 300 toward a distal end of the bracket 300)will cause the solar panel support frame 215 to assume a more verticalorientation. For example, at equatorial latitudes where the sun isnearly directly over-head at noon, the second ball joint 240 should bepositioned in the slot 337 so that the solar panel support frame 215approaches horizontal when the tie-rod 210 is parallel to the mainsupport arm 205; whereas in high latitude regions where the sun remainsat a low azimuth at noon, the second ball joint 240 should be positionedin the slot 337 to provide a greater effective length of the bracket300, which causes the solar panel support frame 215 to assume a morevertical orientation that is normal to the sun.

Further, finer seasonal adjustments of the horizontal orientation of thesolar panel support frame 215 can be made by rotating a nut 350 on thetie-rod 210, which extends or reduces an effective length of the tie rod210.

Referring to FIG. 4, a diagram illustrates a close-up, top view of oneof the pivotable base mechanisms 115-n aligned in the same orientationshown in FIG. 3, according to some embodiments of the present invention.This illustrates the substantially horizontal orientation of the solarpanel support frame 215 compared to the substantially verticalorientation of the solar panel support frame 215 shown in FIG. 2.

Referring to FIG. 5, a diagram illustrates a close-up, rear view of oneof the pivotable base mechanisms 115-n, according to some embodiments ofthe present invention. The solar panel support frame 215 is illustratedin a substantially vertical orientation facing to the East (similar tothe orientation shown in FIGS. 1 and 2). An outline image 500 usingbroken lines then illustrates a comparable substantially verticalorientation of the solar panel support frame 215 facing to the West.

The solar panel array 100 is therefore enabled to cause each solar panel110-n and an associated solar panel support frame 215 to obtain asubstantially vertical orientation in the morning facing the sun on thehorizon in the East. Then, powered by a linear motion of the drive cable120 using the cable actuator 125, each solar panel support frame 215rotates slowly to the North as the main hub 220 rotates, following thearc of the sun during the morning. Simultaneously, each solar panelsupport frame 215 pivots back slowly away from the vertical as the sunrises higher above the horizon. Thus normal vectors extending away fromeach solar panel 110-n remain pointing directly at the sun. Around noon,each solar panel support frame 215 is positioned in its most horizontalorientation (as shown in FIGS. 3 and 4), as the sun is then highest inthe sky. During the afternoon, the main hub 220 continues to rotate andeach solar panel support frame 215 again rises toward a verticalorientation, now facing the West as the sun sets. As will be understoodby those having ordinary skill in the art, the controller 135 can beprogrammed to move the cable actuator 125 according to a simple timer oraccording to a position sensor such as the electronic eye 150.

A length of the tie-bar 210 and/or an effective length of the bracket300, as discussed above, can be periodically and incrementally adjustedto account for seasonal changes in the path of the sun. For example, atthe beginning of a season a configuration of a pivotable base mechanism115-n can be set based on a known arc of the sun during the middle ofthat season. Alternatively, a pivotable base mechanism 115-n can befixed at a single configuration based on an average annual arc of thesun.

Referring to FIG. 6, a diagram illustrates a close-up, side view of apivotable base mechanism 615-n, according to some alternativeembodiments of the present invention. Similar to the pivotable basemechanisms 115-n, the pivotable base mechanism 615-n is shown rotatedrelative to the central support pipe 140 so that the main support arm205 and a tie-rod 610 are both parallel to each other and parallel tothe central support pipe 140 in a vertical plane. A rear pillar mount605 supports a first ball joint 607 above a main hub 620, which enablesthe tie-rod 610 to swing over the main hub 620. A second clamping sleeve612 at a base of the rear pillar mount 605 is used to clamp the rearpillar mount 605 to the central support pipe 140 using bolts 617.Similarly, a clamping sleeve 320 at a base of a hub post 625 of the mainhub 620 is used to clamp the hub post 625 to the central support pipe140 using bolts 330. Thus, according to this alternative embodiment, thetie-rod 610 is connected to the central support pipe 140 independentlyof the main hub 620. The embodiment shown in FIG. 6 thus can bedistinguished from the embodiment shown in FIG. 3, where the tie-rod 210is shown connected through the main hub 220 to the single clampingsleeve 320.

Shown in a partial cut-away view of the main hub 620, bearings 635inside the main hub 620 enable a main support arm 205 to rotate relativeto a hub post 625. Neglecting any minor springing or bending motion ofthe rear pillar mount 605, a distance between the main hub 620 and theswivel end of the tie-rod 610 remains substantially constant when themain hub 620 rotates relative to the central support pipe 140.

The orientation of the pivotable base mechanism 615-n shown in FIG. 6 isused, for example, around noon when the sun is highest in the sky and isshining from the North (when the pivotable base mechanism 615-n isemployed in the southern hemisphere). Depending on the season and thelatitudinal position of the pivotable base mechanism 615-n, increasingthe distance between the rear pillar mount 605 and the main hub 620(e.g., by sliding the second clamping sleeve 612 along the centralsupport pipe 140 away from the clamping sleeve 320) will cause the solarpanel support frame 215 to assume a more horizontal orientation. Forexample, at equatorial latitudes where the sun is nearly directlyover-head at noon, the rear pillar mount 605 should be positioned sothat the solar panel support frame 215 is nearly horizontal when thetie-rod 610 is parallel to the main support arm 205.

Referring to FIG. 7, a diagram illustrates a close-up, partial cut-awayview of the tie-rod 210 or 610, according to some embodiments of thepresent invention. As described above, the tie-rod 210 or 610 cancomprise a linear spring to enable a length of the tie-rod 210 or 610 toincrease or decrease when a high wind force is applied to a solar panel110-n. Such changes in the length of the tie-rod 210 or 610 thus enablea solar panel 110-n to lean over in high wind and significantly reducepotentially damaging wind forces applied to the solar panel 110-n.

As shown, the tie-rod 210 or 610 comprises a damped, two-way, linearspring gas strut 705 bolted into a mounting pipe 710. The mounting pipe710 is then bolted to the tie-rod bracket 239 or to the rear pillarmount 605 through the first ball joint 235 or 607, respectively,depending on various embodiments of the present invention. The gas strut705 includes a first compression chamber 715 in which a gas iscompressed when a tensile force is applied to the strut 705, and asecond compression chamber 720 in which a gas is compressed when acompressive force is applied to the strut 705. A wear ring 725 slidesagainst the strut 705 when the strut 705 moves in and out of themounting pipe 710.

Those skilled in the art will appreciate that various embodiments of thepresent invention can include other types of tie-rods, such as simplerigid tie-rods and tie-rods incorporating various types of springmechanisms such as damped mechanical coil springs and undamped springs.

Various other embodiments and modifications of the present invention arealso enabled by the present disclosure. For example, those skilled inthe art will readily appreciate that various reconfigurations of theembodiments shown in FIGS. 1 through 7 are possible, while stillaccomplishing the features and functions of the solar tracking system ofthe present invention. For example, various relative dimensions of thecomponents of the solar panel array 100 can be changed, and variousalternative types of components can be substituted. For example, variousdifferent fastener and connection mechanisms, including welding andunitary construction of components, can be employed to achieve thefunctionality enabled by the teachings of the present invention.

As will be understood by those having ordinary skill in the art, thesolar panel array 100 also can be mounted in various locations besidesrooftops. For example, the array 100 can be mounted directly on theground, on various stationary structures, or on vehicles, and can bescaled up or down to support different size solar panels.

Further, the embodiments illustrated in the drawings comprise an arrayof multiple solar panels 110-n. However, those having ordinary skill inthe art will readily appreciate that the teachings of the presentinvention also enable construction and use of a single pivotable basemechanism 115-n to track the path of the sun. In such an embodiment, thepulley 225 can be replaced by a direct-drive mechanism such as amotorized sprocket.

The above description of various embodiments of the present invention isprovided for purposes of description to one of ordinary skill in therelated art. It is not intended to be exhaustive or to limit theinvention to a single disclosed embodiment. As mentioned above, numerousalternatives and variations to the present invention will be apparent tothose skilled in the art of the above teaching. Accordingly, while somealternative embodiments have been discussed specifically, otherembodiments will be apparent or relatively easily developed by those ofordinary skill in the art. This patent specification is intended toembrace all alternatives, modifications and variations of the presentinvention that have been discussed herein, and other embodiments thatfall within the spirit and scope of the above described invention.

1. A solar tracking system, comprising: a main support arm having a hubend and a distal end; a rotatable main hub attached to the hub end ofthe main support arm; a support frame rotatably attached to the distalend of the main support arm; and a tie-rod having a swivel end and aframe end, the swivel end rotatably positioned adjacent to the main huband the frame end connected to the support frame above the distal end ofthe main support arm, whereby rotation of the main hub causes a verticalorientation of the support frame to change.
 2. The solar tracking systemaccording to claim 1, wherein the tie-rod comprises a spring mechanism.3. The solar tracking system according to claim 1, wherein the swivelend of the tie-rod is connected to tie-rod bracket extending from acentre post of the main hub, wherein the main hub is rotatable relativeto the centre post.
 4. The solar tracking system according to claim 1,wherein the support frame comprises a solar panel support frame.
 5. Thesolar tracking system according to claim 1, wherein the main hubcomprises a pulley or sprocket for causing rotation of the main hub. 6.The solar tracking system according to claim 1, wherein the solartracking system further comprises an array including a plurality of mainhubs supporting a plurality of support frames, wherein each main hub inthe plurality of main hubs is attached to a central support rail.
 7. Thesolar tracking system according to claim 1, wherein the swivel end ofthe tie-rod is connected to a rear pillar mount.
 8. The solar trackingsystem according to claim 7, wherein the solar tracking system furthercomprises a clamping sleeve for attaching the rear pillar mount to asupport rail, and another clamping sleeve for attaching the main hub tothe support rail.
 9. The solar tracking system according to claim 7,wherein a distance between the main hub and the rear pillar mount isadjustable.
 10. The solar tracking system according to claim 1, whereinthe solar tracking system further comprises a ball joint at the swivelend of the tie-rod and a ball joint at the frame end of the tie-rod. 11.The solar tracking system according to claim 1, wherein a length of thetie-rod is adjustable.
 12. The solar tracking system according to claim1, wherein the solar tracking system further comprises an electric motorto power a drive cable or sprocket engaging the main hub.
 13. The solartracking system according to claim 1, wherein the electric motor iscontrolled by a timer or a position sensor.
 14. The solar trackingsystem according to claim 1, wherein the main support arm, the rotatablemain hub, the support frame, and the tie-rod define a pivotable basemechanism.